1. Field of the Invention
The present invention relates to a normally closed solenoid-operated valve for controlling the flow of fluid such as hydraulic oil or the like in response to an electric command applied to an electromagnetic coil which excites the solenoid-operated valve.
2. Discussion of the Related Art
Heretofore, as normally closed solenoid-operated valves of this type, there has been known one described in the U.S. Pat. No. 5,601,275 to the inventor of the present application. The known valve is provided with a cylindrical sleeve, a stationary element provided at one end of the cylindrical sleeve, a movable element inserted slidably within the sleeve to move relative to the stationary element, and an electromagnetic coil for exciting the stationary element and the movable element. On the external surface of the movable element, there are formed communication grooves, which axially extend between the both ends of the movable element for permitting the flow of operating fluid therethrough.
Further, in the known solenoid-operated valve, a damper chamber and a valve chamber are formed at the axial opposite ends of the movable element, and a sealing member is provided on the external wall surface. At a part of the circumferential surface of the sealing member, a V-groove is formed, by which a throttle passage is constituted to make the valve chamber and the damper chamber communicate with each other.
In the aforementioned solenoid-operated valve, the valve chamber and the damper chamber are in communication only through the fixed throttle passage. Thus, as shown by the broken line in FIG. 4, the throttle area remains invariable or constant regardless of the movement of the movable element, i.e., regardless of whether the movable element comes close to the stationary element or goes away therefrom. This causes a damping effect to act over the entire area in which the movable element (valve member) moves. As a result, a delay takes place in the operation response of the solenoid-operated valve. On the contrary, if preference is taken to the operation responsiveness of the solenoid-operated valve, a problem would arise in that a sufficient damping effect cannot be obtained so that the operation noise cannot be diminished satisfactorily. Further, the use of the sealing member raises another problem in respect of increasing the manufacturing cost.